1. Field of the Invention
The present invention relates to an information regenerating apparatus and an information regenerating method in which a regenerated clock is produced from input data, for example, read out from an optical disk such as digital video disk (DVD) to regenerate input data in synchronization with the regenerated clock.
2. Description of Related Art
FIG. 11 is a constitutional diagram showing a conventional information regenerating apparatus. In FIG. 11, 1 indicates an auto-gain controller (AGC) for adjusting an amplitude of input data (RF) read out from an optical disk. 2 indicates a waveform equalizer (EQ) for reshaping a waveform of the input data. The waveform equalizer 2 is composed of a filter for heightening a gain of an attenuated high-frequency signal component of the input data and a low pass filter for removing an unnecessary high-frequency noise of the input data. 3 indicates a slicer for expressing the input data in binary data to produce regenerated data (DATA). The slicer 3 has a comparator for determining the regenerated data to binary data of xe2x80x9c0xe2x80x9d and xe2x80x9c1xe2x80x9d according to a comparison between the input data and a reference electric potential.
4 indicates a phase comparator for comparing an edge of the regenerated data and a phase of a regenerated clock (CLK) and generating a pulse P or a pulse N according to a degree of a phase advance or a degree of a phase lag. 5 indicates a charge pump (C.P.) for charging a condenser 6 with electric current in response to the inputting of the pulse P to heighten an electric potential of the condenser 6 or discharging electric current from the condenser 6 in response to the inputting of the pulse N to lower an electric potential of the condenser 6. 7 indicates a voltage control oscillator (VCO) which oscillates at a frequency corresponding to the electric potential of the condenser 6 to produce the regenerated clock.
Next, an operation is described.
In an information regenerating apparatus in which data is regenerated from input data read out from an optical disk, it is required to produce a clock which synchronizes with the regenerated data. Therefore, a method, in which a clock is regenerated by controlling a voltage control oscillator according to a phase difference between an edge of the regenerated data and the clock, is generally used.
In FIG. 11, in the auto-gain controller 1, an amplitude of the input data read out from an optical disk is adjusted to a constant value. In the wave form equalizer 2, a wave form of the input data, of which the amplitude is adjusted, is reshaped by heightening a gain of an attenuated high-frequency signal component of the input data and removing an unnecessary high-frequency noise of the input data. In the slicer 3, the input data, of which the waveform is reshaped, is expressed in binary data of xe2x80x9c0xe2x80x9d and xe2x80x9c1xe2x80x9d according to a comparison between the input data and a reference electric potential, and regenerated data is produced.
Also, as to the regeneration of a clock, in the phase comparator 4, an edge of the regenerated data is compared with a phase of a regenerated clock produced in the voltage control oscillator 7, and a pulse P or a pulse N is generated according to a degree of a phase advance or a degree of a phase lag. In the charge pump 5, the condenser 6 is charged with electric current in response to the inputting of the pulse P to heighten an electric potential of the condenser 6, or electric current is discharged from the condenser 6 in response to the inputting of the pulse N to lower an electric potential of the condenser 6. The voltage control oscillator 7 oscillates at a frequency corresponding to the electric potential of the condenser 6 and produces the regenerated clock which is synchronized with the regenerated data.
FIG. 12 is a timing chart showing an operation of the conventional information regenerating apparatus.
As shown in FIG. 12, in cases where a leading edge of the regenerated data (DATA) is earlier than a leading edge of the regenerated clock (CLK), that is, in cases where a phase of the regenerated clock is late, a pulse P is generated to heighten an electric potential (C) of the condenser 6, and a frequency of the regenerated clock is heightened. In contrast, in cases where a leading edge of the regenerated data (DATA) is later than a leading edge of the regenerated clock (CLK), that is, in cases where a phase of the regenerated clock is advanced, a pulse N is generated to lower an electric potential (C) of the condenser 6, and a frequency of the regenerated clock is lowered.
Because the conventional information regenerating apparatus has the above-described configuration, all constituent elements of the conventional information regenerating apparatus are made of analog circuits. However, in cases where a plurality of conventional information regenerating apparatuses are, for example, made of complementary metal oxide semiconductor large scale integrated circuits (CMOS-LSI), because characteristics of p-channel transistors and characteristics of n-channel transistors lack uniformity, the electric currents in the charge pumps 5 of the conventional information regenerating apparatuses lack uniformity and are set to various values. Therefore, a phase lock point of a phase synchronization loop is shifted from a value corresponding to an ideal state, and a clock regeneration characteristic becomes worse. That is, because characteristics of circuit elements of analog circuits lack uniformity, there is a problem that characteristics of the conventional information regenerating apparatuses lack uniformity.
An object of the present invention is to provide, with due consideration to the drawbacks of the conventional information regenerating apparatus, an information regenerating apparatus which is made of digital circuits, is operated at a uniform characteristic and has a high performance. Also, the object of the present invention is to provide an information regenerating method applied for the information regenerating apparatus.
The object is achieved by the provision of an information regenerating apparatus comprising an analog-to-digital converter for converting input data into digital data by performing a data-extraction for the input data in synchronization with a regenerated clock, a zero-cross detector for detecting a zero-cross of the digital data converted in the analog-to-digital converter according to the two pieces of digital data one after another converted in the analog-to-digital converter, a phase detector for detecting a phase shift quantity between a mid point of two data extracting points of two pieces of digital data, which are data-extracted in the analog-to-digital converter before and after the detection of the zero-cross of the digital data performed in the zero-cross detector, and a zero-cross point of the two pieces of digital data in cases where the zero-cross of the digital data is detected in the zero-cross detector, a frequency calculating unit for calculating target oscillation frequency data by adding up the plurality of phase shift quantities detected in the phase detector, a digital-to-analog converter for converting the target oscillation frequency data calculated in the frequency calculating unit into analog data, and a voltage control oscillator for generating the regenerated clock according to the analog data converted in the digital-to-analog converter and providing the regenerated clock for the analog-to-digital converter.
Because the zero-cross detector, the phase detector and the frequency calculating unit arranged between the analog-to-digital converter and the digital-to-analog converter can be made of digital circuits, the information regenerating apparatus does not receive an adverse influence in which characteristics of analog circuits lack uniformity, and the information regenerating apparatus, which is operated at a uniform characteristic and has a high performance, can be obtained.
Also, the phase shift quantity between the mid point of the two data extracting points of the two pieces of digital data, which are data-extracted in the analog-to-digital converter before and after the detection of the zero-cross of the digital data, and the zero-cross point of the two pieces of digital data is detected in the phase detector. Therefore, even though amplitude values of the two pieces of digital data data-extracted in the analog-to-digital converter vary with time, a changing degree of the amplitude of one piece of digital data is equal to that of the other piece of digital data. Accordingly, the phase shift quantity does not receive the adverse influence of the change of the amplitudes of the two pieces of digital data, and the information regenerating apparatus having a high performance can be obtained.
It is preferred that the information regenerating apparatus further comprises a low pass filter for filtering the analog data converted in the digital-to-analog converter and outputting the filtered analog data to the voltage control oscillator.
Therefore, even though the analog data converted in the digital-to-analog converter is changed by stages, the rapid change of the oscillating frequency in the voltage control oscillator 7 can be prevented.
It is also preferred that the information regenerating apparatus further comprises a jitter calculating unit for calculating a jitter quantity of the regenerated clock for the input data according to an average of absolute values of the phase shift quantities detected in the phase detector.
Therefore, the information regenerating apparatus, in which the jitter quantity of the regenerated clock for the input data can be output, can be obtained.
It is also preferred that the information regenerating apparatus further comprises a defect mask circuit for masking the detection of the zero-cross of the digital data performed in the zero-cross detector according to a lack of the input data.
Therefore, an erroneous operation of the frequency calculating unit based on an erroneous detection of the zero-cross of the digital data can be prevented, and the synchronization of the regenerated clock with the input data can be reliably maintained.
The object is also achieved by the provision of an information regenerating method comprising the steps of converting input data into digital data by performing a data-extraction for the input data in synchronization with a regenerated clock, detecting a zero-cross of the digital data according to the two pieces of digital data one after another converted, detecting a phase shift quantity between a mid point of two data extracting points of two pieces of digital data, which are data-extracted before and after the detection of the zero-cross of the digital data, and a zero-cross point of the two pieces of digital data, calculating target oscillation frequency data by adding up the plurality of detected phase shift quantities, converting the calculated target oscillation frequency data into analog data, and generating the regenerated clock according to the converted analog data.
Therefore, the information regenerating method can be performed by using digital circuits, the information regenerating method does not receive an adverse influence that characteristics of analog circuits lack uniformity, and the information regenerating method applied for an information regenerating apparatus, which is operated at a uniform characteristic and has a high performance, can be obtained.
Also, the phase shift quantity between the mid point of the two data extracting points of the two pieces of digital data, which are data-extracted before and after the detection of the zero-cross of the digital data, and the zero-cross point of the two pieces of digital data is detected. Therefore, even though amplitude values of the two pieces of digital data data-extracted vary with time, a changing degree of the amplitude value of one piece of digital data is equal to that of the other piece of digital data. Accordingly, the phase shift quantity does not receive the adverse influence of the change of the amplitude values of the two pieces of digital data, and the information regenerating method applied for an information regenerating apparatus, which has a high performance, can be obtained.